Torsional modes in multimethylammonium halides

Abstract

The inelastic neutron scattering spectra of the multimethyl ammonium halides have been measured and compared with the Raman and infrared spectra of these compounds in the same energy region. From this comparison the internal torsional modes of the methyl groups have been assigned and also, where possible, the whole body librational modes of the multimethylammonium ions. Approximate barriers to methyl group rotation were calculated, as were the top-top interaction terms, and found to be relatively high. Steric effects due to the short C—N bond length, and the influence of the external crystal field were found to be quite important. Evidence for C—HX^– bonding is discussed.